Rei 「令」on Reiwa has meaning of "commanding" or "ordering command." Back in old days, we are talking about 600 - 700 years ago, in Japan characters had close meaning to way it was used in Chinese where in old documents it was used to indicated law and regulation. However, now Rei 「令」 has meaning of "good" or "splendid" as in reimei 「令名」and also used for a title to honor a person such as in reijyou 「令嬢」in Japanese.
Japanese government has indicated Reiwa 「令和」was referenced from Manyoushu 「万葉集」which is an oldest Japanese document written around second half of 7th century to second half of 8th century with collection of Tannka 「短歌」, Japanese short poetry. Reiwa 「令和」was taken from Tannka 「短歌」about plum tree:
「初春の令月にして気淑く風和ぎ梅は鏡前の粉を披き蘭は珮後の香を薫らす」
written in Manyoushu 「万葉集」, as Japanese government has explained to the public.
